Converted tests to Jasmine test framework

Added the Jasmine test framework (no other dependencies).  Converted all
existing tests to Jasmine (note: some messages reported the block as the
key and vice-versa, fixed in the new tests).  Added some test cases for
openpgp.write_encrypted_message(..),
.write_signed_and_encrypted_message(..), and .generate_key_pair(..).